Michigan Technological University’s invisibility cloak researchers have done it again.
They’ve moved the bar on one of the holy grails of physics: making objects invisible.

Just last month, Elena Semouchkina, an associate professor of electrical and computer
engineering at Michigan Tech, and her graduate student, Xiaohui Wang, reported successful
experimental demonstration of the use of non-conductive ceramic metamaterials to cloak
cylindrical objects from microwave-length electromagnetic waves. Previously, Semouchkina
had designed a non-conductive glass metamaterial cloak that worked with infrared
frequency waves, which are shorter than microwaves.

Then, scarcely was the ink dry on their report in the IEEEMicrowave and Wireless Components Letters, a journal published by the Institute of Electrical and Electronics Engineers, when
they developed a different cloaking approach and published it in the American Institute
of Physics journal, Applied Physics Letters.

This time, they used ordinary dielectric materials such as ceramics having differing
dielectric permittivity—a measure of the response of a substance to an electrical
field— instead of metamaterials, which are artificial materials with properties not found
in nature. They found that they were able to cloak larger cylindrical objects and
cloak them more effectively than they had using metamaterials.

This research, just published online and supported by the National Science Foundation
(NSF), also won Wang an honorable mention in an IEEE student papers competition. Wang’s
paper will be listed in the Technical Program Booklet at an upcoming IEEE International
Symposium on Antennas and Propagation. He received $1000 IEEE grant to travel to the
symposium to present this work.

According to their report in the Applied Physics Letters article, Semouchkina and Wang designed a new kind of cloak that uses a very thin
multilayer dielectric coating made of natural material, not metamaterial. They compared
it through mathematical analysis and computer simulations to a metamaterial cloak
of similar size but based on a different principle, called transformation optics.

“The new cloak demonstrated better cloaking efficiency than did a similarly sized
metamaterial cloak designed by using transformation optics relations,” said Semouchkina.

The new cloak outperforms previous cloaks, which caused more reflection and more shadows,
as well as distortion of the electromagnetic waves, the researchers reported. It is
eight to nine times thinner than metamaterial cloaks and much simpler to make, they
noted.

“The multi-layer dielectric cloak could easily be scaled to work in a variety of frequency
ranges,” Semouchkina said. “The design procedure developed in this work could be
used to further advance the cloak parameters and for adjusting it to practical needs.”

Cloaking may sound like a magic trick or something out of a movie, but it could prove
useful in national security, law enforcement or other applications.

Michigan Technological University is a public research university, home to more than
7,000 students from 54 countries. Founded in 1885, the University offers more than
120 undergraduate and graduate degree programs in science and technology, engineering,
forestry, business and economics, health professions, humanities, mathematics, and
social sciences. Our campus in Michigan’s Upper Peninsula overlooks the Keweenaw Waterway
and is just a few miles from Lake Superior.